1. Field of the Invention
The present invention relates generally to Energy Efficient Ethernet (EEE).
2. Background Art
The Energy Efficient Ethernet (EEE) standard, developed by the IEEE 802.3az Task Force, provides an optional mode of operation for Ethernet which allows Ethernet nodes to save power by disabling certain functionality (e.g., transmit and receive functions) over periods of low link utilization. The EEE mode of operation, called Low Power Idle (LPI) mode, can be supported over various Ethernet MAC (Medium Access Control) and PHY (Physical Layer) configurations.
According to the EEE standard, before entering or exiting LPI mode, an Ethernet node informs its link partner(s) that it intends to enter or exit LPI mode by conveying to its link partner a local EEE-defined PHY level signal (loc_lpi_req). The link partner decodes the conveyed signal to generate another EEE-defined PHY level signal (rem_lpi_req) representative of the LPI status of the Ethernet node. In addition, LPI defines a SEND ZERO PHY transmission mode (SEND_Z) that the PHY of an Ethernet node enters when it completes transitioning into LPI mode, and during which the PHY completely ceases transmission on the link.
When the PHY of its link partner enters SEND_Z mode, an Ethernet node cannot determine whether its link partner is still conveying its loc_lpi_req signal or is already sending zeros. Therefore, unless the Ethernet node can quickly determine whether or not its link partner PHY has entered SEND_Z, the Ethernet node will falsely detect rem_lpi_req and accidentally transition out of LPI mode.
Conventional solutions rely on energy detection (either analog or digital) to detect whether the link partner PHY is transmitting energy on the link. If no energy is detected, then it is assumed that the link partner PHY has entered SEND_Z mode. However, for several reasons, conventional solutions are impractical. For example, solutions based on analog energy detection falsely detect energy on the link because of echo and crosstalk from the local transmitter. On the other hand, digital energy detection solutions first remove the echo and crosstalk, but suffer from latency associated with removing echo and crosstalk, which can be too high to avoid false detection of rem_lpi_req. In addition, even when SEND_Z is detected correctly, conventional solutions require that detection of rem_lpi_req be disabled during SEND_Z mode to avoid false detection of rem_lpi_req and accidental transitioning out of LPI mode by the PHY.
Accordingly, new solutions are needed to detect rem_lpi_req and SEND_Z mode, which do not suffer from the problems described above of conventional solutions.